Method of manufacturing a semiconductor device having vertical transistor with tubular double-gate

ABSTRACT

A semiconductor device allowing control of its threshold voltage without requiring change in the materials of its gate electrodes and suitable for high density integration is disclosed. The semiconductor device includes a p type monocrystalline silicon substrate 1 having a cylindrical portion with inner and outer surfaces and extending in a vertical direction. A first gate electrode 8 and a second gate electrode 10 are disposed at the inner surface and the outer surface of the cylindrical portion 2, respectively. A source/drain region 5 is formed on the top end of the cylindrical portion 2, while a source/drain region 3 is formed on the inner bottom surface of the cylindrical portion 2. Therefore, the cylindrical portion 2 can be utilized as a channel region of an MIS field effect transistor. The threshold voltage of the transistor can easily be controlled by applying separate voltages to the two gate electrodes, the first electrode and the second electrode.

This application is a division of application Ser. No. 08/069,036 filedMay 28, 1993 now U.S. Pat. No. 5,382,816.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to semiconductor devices andmanufacturing methods thereof, and more specifically, to a semiconductordevice having a vertical field effect transistor and a manufacturingmethod thereof.

2. Description of the Background Art

Conventionally, SGTs (Surrounding Gate Transistors) are known asvertical field effect transistors. They are disclosed, for example, inan article entitled "High Performance CMOS Surrounding Gate Transistor(SGT) for Ultra High Density LSIs", IEDM88 Technical Digest, pp 222-225.FIG. 64 is a plan view showing a conventional SGT disclosed therein.FIG. 65 is a cross sectional view showing the SGT in FIG. 64 taken alongline X--X. Referring to FIGS. 64 and 65, the conventional SGT includes asilicon substrate 301, a silicon pillar 301a formed in a prescribedregion on the silicon substrate 301 and extending in a directionvertical to a main surface of the silicon substrate 301, a P well 302formed on the main surface of the silicon substrate 301 and having aprescribed depth, a pair of n type source regions 303 formed in the partof the main surface of the silicon substrate adjacent to the siliconpillar 301a, an n type drain region 304 formed on the top end of thesilicon pillar 301a, and a gate electrode 306 formed on the outerperipheral surface of the silicon pillar 301a with a gate oxide film 305therebetween. The sidewalls of the silicon pillar 301a positionedbetween the source region 303 and the drain region 304 constitute thechannel region of the SGT. More specifically, the channel length L ofthe SGT is defined by the height of the silicon pillar 301a, and thechannel width of the SGT is defined by the outer peripheral length ofthe silicon pillar 301a. In this manner, in the conventional SGT, thesidewalls of the silicon pillar 301a can be used as the channel region,area occupied by the elements can be reduced as compared to aconventional planar type transistor. In other words, the SGT is anelement suitable for high density integration.

The conventional SGT however suffers from the following disadvantage.

As the length t of the silicon pillar 301a in a direction along the mainsurface of the silicon substrate 301 shown in FIG. 65 is shortened withincrease of the integration densities of devices, it will be difficultto control the threshold voltage of the SGT by channel doping. Thisphenomenon is described in detail, for example, in IEEE TRANSACTION OFELECTRON, VOL. ED-30, No. 10, October 1983 CHAPTER III (pp. 1247-1250).As described above, in the conventional SGT, it will be difficultcontrol its threshold voltage by channel doping with the sizes ofelements being reduced, impeding accurate control of the thresholdvoltage as a result.

A conventional method of controlling the threshold voltage by changingthe material of a gate electrode has been proposed. Such a method isdisclosed in Physics of Semiconductor Devices SECOND EDITION by S. M.Sze pp. 363-397 (Table 3 (p. 396)). In this document, a proposed methodcontrols the threshold voltage by using a gate electrode of Au or thelike rather than a conventional gate electrode of polycrystallinesilicon. According to this method, it is principly possible to controlthe threshold voltage.

However, Au used for the gate electrode can contaminate environment in aclean room free of heavy metals which is suitable for manufacturingsilicon semiconductors. Furthermore, a gate electrode of Au is lesssuitable for mass production as compared to a gate electrode ofpolysilicon. On top of that, it is technically difficult to manufacturea gate electrode of Au or the like.

As described above, the conventional method of controlling the thresholdvoltage using a gate electrode formed of Au or the like is principlypossible, but still encountered with various problems in practice. As aresult, it has been difficult to accurately control the thresholdvoltage of an SGT in practice when the sizes of its elements arereduced.

SUMMARY OF THE INVENTION

It is an object of the invention to readily control a threshold voltagewithout changing the material of a gate electrode, in a semiconductordevice.

Another object of the invention is to achieve high density integrationin a semiconductor device.

A further object of the invention is to readily manufacture asemiconductor device allowing easy control of a threshold voltagewithout changing the material of a gate electrode, in a manufacturingmethod of a semiconductor device.

A semiconductor device, in one aspect of the invention, includes asemiconductor substrate of first type conductivity having a standingwall portion having inner and outer surfaces and extending to take atubular shape, a first gate electrode of a tubular shape formed on theinner surface of the standing wall portion with a gate insulating filmtherebetween, a second gate electrode of a tubular shape formed on theouter surface of the standing wall portion with a second gate insulatingfilm therebetween, first source/drain regions of second typeconductivity formed on the top end of the standing wall portion, andsecond source/drain regions of the second type conductivity formed onthe bottom surface of the semiconductor substrate surrounded by theinner surface of the standing wall portion.

The first gate electrode of tubular shape is formed on the inner surfaceof the standing wall of the semiconductor substrate of the first typeconductivity extending in a tubular manner with the first gateinsulating film therebetween, the second gate electrode of tubular shapeis formed on the outer surface of the standing wall with the second gateinsulating film therebetween, and, therefore, separate voltages canreadily be applied to the first gate electrode and the second gateelectrode. Accordingly, controlling voltages applied to the first gateelectrode and the second gate electrode provides easy control of thethreshold voltage without requiring change of the materials of the gateelectrodes. Furthermore, since the semiconductor device is a verticalsemiconductor device whose standing wall portion functions as a channelregion, area occupied by its elements can be reduced as compared toconventional planar type semiconductor devices.

The semiconductor device, in another aspect of the invention, includes asemiconductor substrate of first type conductivity having a standingwall portion having inner and outer surfaces and extending in a tubularmanner, a first gate electrode formed on the inner surface of thestanding wall portion with a first gate insulating film therebetween, asecond gate electrode formed on the outer surface of the standing wallportion with a second gate insulting film therebetween, firstsource/drain regions of second type conductivity formed on the top endof the standing wall portion, second source/drain regions of the secondtype conductivity formed on the bottom surface of the semiconductorsubstrate surrounded by the inner surface of the standing wall portion,a capacitor lower electrode electrically connected to the secondsource/drain regions, and a capacitor upper electrode formed on thecapacitor lower electrode with a capacitor insulating film therebetween.

The first gate electrode is formed on the inner surface of the standingwall portion of the semiconductor substrate extending in a tubularmanner with a first insulating film therebetween, the second gateelectrode is formed on the outer surface of the standing wall portionwith a second gate insulating film therebetween, and, therefore,controlling voltages applied to the first gate electrode and the secondgate electrode at respective prescribed values provides easy control ofthe threshold voltages without requiring change of materials of the gateelectrodes. Furthermore, since the standing wall portion functions as achannel region, thereby forming a vertical semiconductor device, areaoccupied by its elements can be reduced as compared to conventionalplanar type semiconductor devices. The second source/drain regions areformed on the bottom surface of the semiconductor substrate surroundedby the inner surface of the standing wall portion, the capacitor formedof the capacitor lower electrode, the capacitor insulating film and thecapacitor upper electrode is electrically connected to the secondsource/drain regions, and, therefore, higher density integration can beachieved as compared to conventional planar type semiconductor devicesincluding transistors and capacitors.

A method of manufacturing a semiconductor device, in a still furtheraspect of the invention, includes the steps of forming a standing wallportion having inner and outer surfaces extending in a tubular manner ona main surface of a semiconductor substrate of first type conductivity,forming a first gate electrode of a tubular shape on the inner surfaceof the standing wall portion with a first gate insulating filmtherebetween, a second gate electrode of a tubular shape on the outersurface of the standing wall portion with a second gate insulating filmtherebetween, forming first source/drain regions by implanting animpurity of second type conductivity to the top end of the standing wallportion, and forming second source/drain regions by implanting animpurity of the second type conductivity to the bottom surface of thesemiconductor substrate surrounded by the inner surface of the standingwall.

The standing wall having inner and outer surfaces and extending in atubular manner is formed on a main surface of the semiconductorsubstrate of the first type conductivity, the first gate electrode of atubular shape is formed on the inner surface of the standing wallportion with the first gate insulating film therebetween, the secondgate electrode of a tubular shape is formed on the outer surface of thestanding wall portion with the second gate insulating film therebetween,the first source/drain regions are formed by implanting the impurity ofthe second type conductivity to the top end of the standing wallportion, and the second source/drain regions are formed by implantingthe impurity of the second type conductivity to the bottom surface ofthe semiconductor substrate surrounded by the inner surface of thestanding wall portion, and, therefore, the vertical type semiconductordevice whose standing wall portion functions as a channel regions canreadily be manufactured. Furthermore, the vertical type semiconductordevice having the first gate electrode and the second gate electrode canreadily be manufactured.

The method of manufacturing the semiconductor device, in yet anotheraspect of the invention, includes the steps of forming a standing wallportion having inner and outer surfaces and extending in a tubularmanner on a main surface of a semiconductor substrate of first typeconductivity, forming a first gate electrode of a tubular shape on theinner surface of the standing wall portion with a first gate insulatingfilm therebetween, forming a second gate electrode of a tubular shape onthe outer surface of the standing wall portion with a second gateinsulating film therebetween, forming first source/drain regions byimplanting an impurity of second type conductivity to the top end of thestanding wall portion, forming second source/drain regions by implantingan impurity of the second type conductivity on the bottom surface of thesemiconductor substrate surrounded by the inner surface of the standingwall portion, forming a capacitor lower electrode to be electricallyconnected to the second source/drain regions, and forming a capacitorupper electrode on the capacitor lower electrode with a capacitorinsulating film therebetween.

Since the standing wall portion having the inner and outer surfaces andextending in a tubular manner is formed on the main surface of thesemiconductor substrate of the first type conductivity, the first gateelectrode of a tubular shape is formed on the inner surface of thestanding wall portion with the first gate insulating film therebetween,the second gate electrode of a tubular shape is formed on the outersurface of the standing wall portion with the second gate insulatingfilm therebetween, the first source/drain regions are formed byimplanting the impurity of the second type conductivity to the top endof the standing wall portion, the second source/drain regions are formedby implanting the impurity of the second type conductivity onto thebottom surface of the semiconductor substrate surrounded by the innersurface of the standing wall portion, the capacitor lower electrode isformed to be electrically connected to the second source/drain regions,and the capacitor upper electrode is formed on the capacitor lowerelectrode with the capacitor insulating film therebetween, the verticaltype semiconductor device whose standing wall portion functions as achannel region can readily be manufactured. Furthermore, the verticalsemiconductor device having two gate electrodes, the first gateelectrode and the second gate electrode can readily be manufactured.Furthermore, the capacitor formed of the capacitor lower electrode, thecapacitor insulating film, and the capacitor upper electrode iselectrically connected to the second source/drain regions, and,therefore, the semiconductor device having a storage region suitable forhigh density integration can readily be manufactured.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing an MIS type semiconductor device (an MIStype field effect transistor) in accordance with a first embodiment ofthe invention;

FIG. 2 is a cross sectional view showing the structure of the MIS typesemiconductor device in accordance with the first embodiment shown inFIG. 1 taken along line X--X;

FIG. 3 is a cross sectional view showing the structure of the MIS typefield effect transistor in accordance with the first embodiment shown inFIG. 1 taken along line Y--Y;

FIGS. 4-43 are cross sectional views showing steps (1st-39th) in amanufacturing process of the MIS type field effect transistor inaccordance with the first embodiment shown in FIG. 2;

FIG. 44 is a cross sectional view for use in illustration of the 39thstep in a manufacturing process of the MIS type field effect transistorof the first embodiment shown in FIG. 3;

FIG. 45 is a plan view showing an EE type static inverter formed usingtwo vertical type MIS type field effect transistors in accordance with asecond embodiment of the invention;

FIG. 46 is an equivalent circuit diagram showing the EE type staticinverter in accordance with the second embodiment shown in FIG. 45;

FIG. 47 is a plan view showing a DRAM having a vertical type MIS fieldeffect transistor and a capacitor in accordance with a third embodimentof the invention;

FIG. 48 is a cross sectional view showing the structure of the DRAM inaccordance with the third embodiment shown in FIG. 47 taken along lineX--X;

FIG. 49 is a cross sectional view showing the structure of the DRAM inaccordance with the third embodiment shown in FIG. 47 taken along lineY--Y;

FIG. 50 is an equivalent circuit diagram showing the memory cell portionof the DRAM in accordance with the third embodiment shown in FIG. 47;

FIG. 51 is a plan view showing arrangement of a plurality of the memorycells constituting the DRAM in accordance with the third embodimentshown in FIG. 47;

FIGS. 52-62 are cross sectional views for use in illustration of steps(18th-28th) in a manufacturing process of the DRAM in accordance withthe third embodiment shown in FIG. 48;

FIG. 63 is a cross sectional view showing the 28th step in amanufacturing process of the DRAM in accordance with the thirdembodiment shown in FIG. 49;

FIG. 64 is a plan view showing a conventional SGT as an example of avertical type MIS semiconductor device; and

FIG. 65 is a cross sectional view showing the structure of theconventional SGT shown in FIG. 64 taken along line X--X.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in conjunctionwith the appended drawings.

FIG. 1 is a plan view showing a vertical type MIS semiconductor device(MIS field effect transistor) in accordance with a first embodiment ofthe invention. FIG. 2 is a cross section view showing the structure ofthe MIS semiconductor device shown in FIG. 1 taken along line X--X.

FIG. 3 is a cross sectional view showing the structure of the MISsemiconductor device shown in FIG. 1 taken along line Y--Y.

Referring to FIGS. 1-3, the vertical type MIS semiconductor device inaccordance with the first embodiment includes a p type monocrystallinesilicon substrate 1, a cylindrical portion (standing wall portion) 2 ofmonocrystalline silicon and extending from a prescribed region on a mainsurface of the P type monocrystalline silicon substrate 1 in a directionvertical to the main surface of the p type monocrystalline siliconsubstrate 1, a first gate electrode 8 of polysilicon formed on the innersurface of the cylindrical portion 2 with a first gate oxide film 7 ofSiO₂ therebetween, a second gate electrode 10 of polycrystalline siliconformed on the outer surface of the cylindrical portion 2 with a secondgate oxide film 9 of SiO₂ therebetween, highly concentrated n typesource/drain regions 5a formed on the top end of the cylindrical portion2, n type source/drain regions 5b of a low concentration serially formedon the ends of the source/drain regions 5a, highly concentrated n typesource/drain region 3 formed on the bottom surface of the p typemonocrystalline silicon substrate 1 surrounded by the inner surface ofthe cylindrical portion 2, n type source/drain regions 4 of a lowconcentration serially formed on the opposite ends of the source/drainregion 3, and a p⁺ impurity region 6 formed on the main surface of the ptype monocrystalline silicon substrate 1 a prescribed distance apartfrom the cylindrical portion 2 for fixing the potential of the substrateand isolating elements. The source/drain regions 5a and 5b, thesource/drain regions 3 and 4, the cylindrical portion 2, the first gateelectrode 8, and the second gate electrode 10 constitute a vertical typefield effect transistor (FET).

Electrically connected to the source/drain region 3 is aninterconnection layer 11. An interconnection layer 12 is electricallyconnected to the p⁺ impurity region 6. Conductive layers 15a, 15b, and15c are formed on the source/drain regions 5a, 5b, the interconnectionlayer 11, and the interconnection layer 12, respectively. An insulatingfilm 16 of a silicon nitride film is formed on the conductive layers15a, 15b, and 15c. An interlayer insulating film 13 of SiO₂ is formedbetween the interconnection layer 12 and the second gate electrode 10.An interlayer insulating film 14 of SiO₂ is formed between theinterconnection layer 11 and the first gate electrode 10. An interlayerinsulating film 14 of SiO₂ is formed between the interconnection layer11 and the first gate electrode 8. An interconnection layer 18 iselectrically connected to the first gate electrode 8 with aninterconnection layer 17 being electrically connected to the secondelectrode 10. An interlayer insulating film 19 having contact holes 19a,19b, and 19c is formed covering the interconnection layer 17, theconductive layer 15, and the interconnection layer 18. A metalinterconnection layer 20 is formed to be electrically connected to theinterconnection layer 17 in the contact hole 19a and to extend along thesurface of the interlayer insulating film 19. A metal interconnectionlayer 22 is formed to be electrically connected to the conductive layer15 in the contact hole 19b. A metal interconnection layer 21 is formedto be electrically connected to the interconnection layer 18 in thecontact hole 19c and to extend along the surface of the interlayerinsulating film 19.

As shown in FIG. 3, a metal interconnection layer 23 is electricallyconnected to the conductive layer 15a formed on the source/drain region5a through a contact hole 19d. A metal interconnection layer 24 iselectrically connected to the conductive layer 15c formed on theinterconnection layer 12 through a contact hole 19e. The interconnectionlayers 11, 12, 17, and 18 are all formed of polycrystalline silicon. Theconductors 15a, 15b, 15c are all formed of polycrystalline silicon. Themetal interconnection layers 20, 21, 22, 23, and 24 are formed ofaluminum or the like.

As described above, in this embodiment, the cylindrical portion 2 formedextending in the vertical direction from the prescribed region on themain surface of the p type monocrystalline silicon substrate 1 is usedas the channel region of the FET. The threshold voltage of the FET iscontrolled by two gate electrodes, i.e. the first gate electrode 8formed on the inner surface of the cylindrical portion 2 and the secondelectrode 10 formed on the outer surface of the cylindrical portion 2.More specifically, setting a voltage applied to the first gate electrode8 and a voltage applied to the second gate electrode 10 to be respectiveprescribed values provides easy and accurate control of the thresholdvoltage without requiring change of the materials of the gate electrodesas have been conventionally practiced. Principles and a method ofcontrolling threshold voltage using two gate electrodes are disclosedin, for example, an article entitled "High Performance Characteristicsin Trench Dual-Gate MOSFET (TDMOS)", IEEE ED VOL. 38, No. 9, September1991, pp. 2121-2127.

More specifically, the first gate electrode 8 is used as a main gate,and the second electrode 10 is used as a sub gate. Under such acondition, when the voltage of the second gate electrode (sub gate) 10is fixed to 0 V, the threshold voltage V_(TH) becomes 0.6 V. When thesecond gate electrode (sub gate) 10 is fixed to -0.4 V, the thresholdvoltage V_(TH) becomes 0.8 V. More specifically, the threshold voltagecan readily be controlled by applying to the second gate electrode (subgate) 10, the negative voltage (-0.4 V) of a voltage (0.4 V)corresponding to twice the amount of the threshold voltage desired to bechanged (0.2 V). Furthermore, according to the method of controlling thethreshold voltage by the two gate electrodes, the first gate electrode 8and the second gate electrode 10 as described above, the thresholdvoltage can be controlled after completion of the elements as opposed toconventional methods. Thus, the threshold voltage can be controlleddepending upon the levels of noises included in an input signal.

In this embodiment, since the sidewall portion of the cylindricalportion 2 of monocrystalline silicon is used as the channel region, areaoccupied by the elements can be reduced as compared to conventionalplanar type (plane type) transistors. Consequently, MIS typesemiconductor devices suitable for high density integration can beprovided. Furthermore, the p⁺ impurity region 6 for fixing the potentialof the substrate can also be used for element isolation, it will not benecessary to form an LOCOS (Local Oxidation of Silicon) oxide film forelement isolation. As a result, the semiconductor device of thisembodiment will not suffer from the disadvantage that the isolationregion is expanded by the bird's beaks of an LOCOS oxide film when theLOCOS oxide film is used for element isolation. Therefore, in thestructure of this embodiment shown in FIGS. 2 and 3, integration densitycan be increased as compared to the one employing the LOCOS oxide filmfor element isolation.

Furthermore, a complete depletion type FET, the cylindrical portion 2 ofwhich is entirely depleted can be formed by reducing the thickness ofthe cylindrical portion 2. Such a complete depletion type FET providesgood switching characteristics. This makes it possible to set thethreshold voltage of the FET to a low level. In the MIS typesemiconductor device in accordance with this embodiment, the thresholdvoltage can readily be controlled by the first gate electrode 8 and thesecond gate electrode 10, and, therefore, there will not be any problemif the threshold voltage can not be controlled by channel doping withthe thickness of the cylindrical portion 2 being reduced.

FIGS. 4-44 are cross sectional views for use in illustration of amanufacturing process of the MIS type semiconductor device in accordancewith the first embodiment shown in FIGS. 1-3. Referring to FIGS. 1-3 andFIGS. 4-44, a description of the manufacturing process of the MIS typesemiconductor device in accordance with the first embodiment follows.

As shown in FIG. 4, a silicon oxide film (SiO₂) 31 is formed on a p typemonocrystalline silicon substrate 1. A silicon nitride film (Si₃ N₄) isformed on the silicon oxide film 31.

Then, as shown in FIG. 5, cylindrical resist 33 is formed in aprescribed region on the silicon nitride film 32 by means of aphotolithography technique. The silicon nitride film 32 and the siliconoxide film 31 are anisotropically etched using the cylindrical resist 33as mask to form a cylindrical silicon nitride film 32 and a siliconoxide film 31. Then, the resist 33 is removed away.

Then, as shown in FIG. 6, the p type monocrystalline silicon substrate 1is anisotropically etched, using as mask the cylindrical silicon nitridefilm 32 and the silicon oxide film 31, and a cylindrical portion 2 isformed.

As shown in FIG. 7, a thermal oxide film 34 of SiO₂ is formed on a mainsurface of the p type monocrystalline silicon substrate 1, while a firstgate oxide film 7 and a second gate oxide film 9 both of SiO₂ are formedon the inner surface and the outer surface of the cylindrical portion 2,respectively.

As shown in FIG. 8, a polycrystalline silicon film 35 is formed to coverthe p type monocrystalline silicon substrate 1 and the cylindricalportion 2 by means of Chemical Vapor Deposition.

As shown in FIG. 9, the surface of the polycrystalline silicon film 35is planarized by means of a polishing method or a resist etch backmethod. Thereafter, the polycrystalline silicon film 35 is etched backto a prescribed thickness so that the upper portion of the cylindricalportion 2 is exposed.

Then, as shown in FIG. 10, a silicon oxide film 36 is formed on theentire surface by means of CVD. A silicon nitride film 37 is formed onthe silicon oxide film 36.

As shown in FIG. 11, a silicon oxide film 38 is formed so that only thesilicon oxide film 37 positioned in the upper part of the cylindricalportion 2 is exposed and the entire surface is planarized.

As shown in FIG. 12, the exposed silicon nitride film 37 positioned inthe upper part of the cylindrical portion 2 is removed away by achemical treatment.

As shown in FIG. 13, the silicon oxide film 38 (see FIG. 12) is entirelyetched away, and the silicon oxide film 36 positioned in the upper partand the upper side end portion of the cylindrical portion 2 is etchedaway.

As shown in FIG. 14, a silicon nitride film 39 is formed on the entiresurface.

As shown in FIG. 15, the entire surface of the silicon nitride film 39is anisotropically etched, and a sidewall 39a of a silicon nitride filmis formed on the upper sidewall portion of the cylindrical portion 2.The upper part of the cylindrical portion 2 is surrounded by the siliconnitride film 32 and the sidewall 39a of silicon nitride film.

As shown in FIG. 16, using as mask the silicon nitride film 32 and thesidewall 39a of silicon nitride film, the silicon oxide film 36 and thepolycrystalline silicon film 35 are etched. Thus, the first gateelectrode 8 of a cylindrical shape is formed on the inner surface of thecylindrical portion 2 with the first gate oxide film 7 therebetween, andthe second gate electrode 10 of a cylindrical shape is formed on theouter surface of the cylindrical portion 2 with the second gate oxidefilm 9 therebetween.

As shown in FIG. 17, resist 40 covering the outside of the cylindricalportion 2 is formed by means of a photolithography technique. Impurityions of n type are implanted into the p type monocrystalline siliconsubstrate 1, using the resist 40, the silicon nitride film 32, and thesidewall 39a as mask. Thus, the n type source/drain region 4 of a lowimpurity concentration is formed. Then, the resist 40 is removed away.

As shown in FIG. 18, a silicon oxide film 41 is formed to cover theentire surface by means of CVD.

As shown in FIG. 19, after the surface of the silicon oxide film isplanarized, the silicon oxide film 41 is etched back until the siliconnitride film 32 and the sidewall 39 are exposed.

As shown in FIG. 20, a silicon nitride film 42 is formed on the entiresurface.

As shown in FIG. 21, the silicon nitride film 42 (see FIG. 20) isanisotropically etched, and a sidewall 42a formed of a silicon nitridefilm is formed on the sidewall portion of the sidewall 39a of siliconnitride film.

As shown in FIG. 22, using as mask the silicon nitride film 32, thesidewall 39a of silicon nitride film, and the sidewall 42a, the siliconoxide film 41 is etched. Thus, the interlayer insulating film 14 of asilicon oxide film is formed on the inner surface of the first gateelectrode 8, and the interlayer insulating film 13 formed of siliconoxide film is formed on the outer surface of the second gate electrode10.

As shown in FIG. 23, resist 43 covering the outside of the cylindricalportion 2 is formed by means of a photolithography technique. Using asmask the resist 43, the silicon nitride film 32, the sidewalls 39a and42a, n type impurity ions are implanted into the p type monocrystallinesilicon substrate 1, and the highly concentrated n type source/drainregions 3 are formed. Thereafter, the resist 43 is removed away.

As shown in FIG. 24, resist 44 covering the inside of the cylindricalportion 2 is formed by means of a photolithography technique. Using theresist 44, the silicon nitride film 32, and the sidewalls 39a and 42a asmask, p type impurity ions are implanted into the p type monocrystallinesilicon substrate 1, and the p⁺ impurity region 6 is formed on the outerbottom portion of the cylindrical portion 2. The p⁺ impurity region 6fixes the potential of the substrate and has a function of isolatingelements. Thereafter, the resist 44 is removed away.

Then, as shown in FIG. 25, a polycrystalline silicon film 45 is formedon the entire surface by means of CVD.

Then, as shown in FIG. 26, after planarizing the surface of thepolycrystalline silicon film 45, the polycrystalline silicon film 45 isetched back until the silicon nitride film 32, the sidewall 39a, and thesidewall 42a are exposed. Thus, the interconnection layer 11 connectedto the source/drain region 3 and the interconnection layer 12 connectedto the p⁺ impurity region 6 are formed.

Then, as shown in FIG. 27, resist 46 covering the outside of thecylindrical portion 2 is formed by means of a photolithographytechnique. Using the resist 46 as mask, n type impurity ions areimplanted into the interconnection layer 11. Thereafter, the resist 46is removed away.

Then, as shown in FIG. 28, resist 47 covering the inside of thecylindrical portion 2 is formed by means of a photolithographytechnique. Using the resist 47 as mask, p type impurity ions areimplanted into the interconnection layer 12. Thereafter, the resist 47is removed away.

Then, as shown in FIG. 29, the silicon nitride film 32 (see FIG. 28) andthe sidewalls 39a and 42a of silicon nitride films (see FIG. 28) areremoved away.

Then, as shown in FIG. 30, resist 48 is formed to cover theinterconnection layer 12 by means of a photolithography technique. Usingthe resist 48 as mask, n type impurity ions are implanted into the upperend portion of the cylindrical portion 2, and the n type source/drainregions 5b of a low impurity concentration, and n type highlyconcentrated source/drain regions 5a are formed. Thereafter, the resist48 is removed away.

A shown in FIG. 31, the silicon oxide film 31 (see FIG. 30) is removedaway by a chemical treatment. A polycrystalline silicon film 15 isformed on the entire surface by means of chemical vapor deposition. Asilicon nitride film 16 is formed on the polycrystalline silicon film15. Then, as shown in FIG. 32, resist 49 is formed in the upper part ofthe interconnection layer 12 and in the upper part of the cylindricalportion 2 by means of a photolithography technique.

Then, as shown in FIG. 33, using resist 49 (see FIG. 32) as mask, thesilicon nitride film 16 and the polycrystalline silicon film 15 areetched. Thus, the conductive layers 15a, 15b, and 15c are formed.

Now, as shown in FIG. 34, a silicon oxide film 50 is formed to cover theentire surface by means of CVD.

As shown in FIG. 35, resist 51 having a contact hole pattern is formedin a prescribed region on the silicon oxide film 50 by means of aphotolithography technique.

As shown in FIG. 36, using the resist 51 (see FIG. 35) as mask, thesilicon oxide film 50, and the interlayer insulating films 13 and 14 ofsilicon oxide film are etched to form the contact holes 50a and 50b in aself-alignment manner. Thereafter, the resist 51 is removed away.

As shown in FIG. 37, a polycrystalline silicon film 52 is formed on theentire surface by means of chemical vapor deposition.

As shown in FIG. 38, resist 53 is formed in a prescribed region on thepolycrystalline silicon film 52 by means of a photolithographytechnique. Using the resist 53 as mask, the polycrystalline silicon film52 is etched. Thus, as shown in FIG. 39, the interconnection layer 18connected to the first gate electrode 8, and the interconnection layer17 connected to the second gate electrode 10 are formed. Thereafter, theresist 53 is removed away.

As shown in FIG. 40, the interlayer insulating film 19 of silicon oxidefilm is formed on the entire surface by means of CVD.

Then, as shown in FIG. 41 (cross section along X--X) and FIG. 42 (crosssection along Y--Y), resist 54 having a contact hole pattern in theupper part of the interconnection layers 11 and 12 and in the upper partof the cylindrical portion 2 is formed.

Then, as shown in FIG. 43 and 44, using the resist 54 as mask, theinterlayer insulating film 19 of silicon oxide film is etched to formthe contact holes 19a, 19b, 19c, 19d, and 19e for establishingelectrical contacts with the interconnection layer 17, theinterconnection layer 11, the interconnection layer 18, the cylindricalportion 2, and the interconnection layer 12, respectively.

Finally, as shown in FIGS. 2 and 3, the interconnection layers 20, 22,21, 23, and 24 in electrical connection with the interconnection layer17, the conductive layer 15b, the interconnection layer 18, thesource/drain regions 5 and the interconnection layer 12, respectivelyare formed.

Thus, the vertical type MIS semiconductor device of the first embodimentis completed.

FIG. 45 is a plan view showing arrangement of an EE type static inverterformed using two MIS field effect transistors in accordance with asecond embodiment of the invention. FIG. 46 is an equivalent circuitdiagram showing the EE type static inverter shown in FIG. 45. Referringto FIGS. 45 and 46, the EE type static inverter in accordance with thesecond embodiment is formed of a combination of two MIS field effecttransistors shown in FIGS. 1-3. More specifically, the EE type staticinverter in accordance with the second embodiment includes an N channelMIS field effect transistor 60, and an N channel MIS field effecttransistor 70. A source/drain region 63 of the MIS field effecttransistor 60 and a source/drain region 73 of the MIS field effecttransistor 70 are mutually connected and connected together to an outputterminal V_(out). A source/drain region 61 of the MIS field effecttransistor 60 is connected to a V_(CC) power supply. The first gateelectrode 62 of the MIS field effect transistor 60 is connected to thesource/drain region 61. The second gate electrode 64 of the MIS fieldeffect transistor 60 and the second gate electrode (sub gate electrode)of the MIS field effect transistor 70 are mutually connected andconnected together to a V_(G2) power supply. A source/drain region 71 ofthe MIS field effect transistor 70 is grounded, with the first gateelectrode 72 being connected to an input power supply V_(IN). The MISfield effect transistors 60 and 70 are supplied with a back gate voltageV_(BB). In the EE type static inverter in accordance with the secondembodiment having such a structure, the threshold voltages of the MISfield effect transistors 60 and 70 can readily be controlled bycontrolling the voltage V_(G2) applied to the second gate electrodes(sub gate electrodes) 64 and 74. This makes it possible to control thethreshold voltages depending upon the noise levels of signals, thusproviding transistor characteristics suitable for various operationstates. The broken line in FIG. 45 represents the boundaries of theregions occupied by the field effect transistors. Thus arranging the MISfield effect transistor in the center of a regular hexagon permits onesuch MIS field effect transistor to be surrounded by six MIS fieldeffect transistors. More specifically, a so-called "closest packedstructure" most suitable for high density integration is provided.

FIG. 47 is a plan view showing a memory cell in a DRAM employing avertical type MIS field effect transistor in accordance with a thirdembodiment of the invention. FIG. 48 is a cross sectional view showingthe DRAM shown in FIG. 47 taken along line X--X. FIG. 49 is a crosssectional view showing the DRAM in FIG. 47 taken along line Y--Y. FIG.50 is an equivalent circuit diagram showing the memory cell portion ofthe DRAM shown in FIGS. 47-49.

Referring to FIGS. 47-50, the DRAM in accordance with the thirdembodiment includes a p type polycrystalline silicon substrate 1, acylindrical portion 2 formed of polycrystalline silicon and extendingfrom a prescribed region on a main surface of the p type monocrystallinesilicon substrate 1 in the direction vertical to the main surface, afirst cylindrical gate electrode 8 of polycrystalline silicon formed onthe inner surface of the cylindrical portion 2 with a gate oxide film 7of SiO₂ therebetween, a second cylindrical gate electrode (sub gateelectrode) 1 formed on the outer surface of the cylindrical portion 2with a second gate oxide film 9 of SiO₂ therebetween, an n typesource/drain region of a low impurity concentration formed on the bottomsurface portion of the p type monocrystalline silicon substrate 1surrounded by the inner surface of the cylindrical portion 2, an n typecylindrical source/drain region 5 having a high impurity concentrationformed on the top ends of the cylindrical portion 2, a cylindricalcapacitor lower electrode (storage node) 81 electrically connected tothe source/drain region 4 and formed to extend upwardly, a capacitorupper electrode (cell plate) 83 formed to be buried in the cylindricalinside portion of the storage node 81 with a capacitor insulating film82 therebetween, a p⁺ impurity region 6 formed in a prescribed region ona main surface of the p type monocrystalline silicon substrate 1positioned outside the cylindrical portion 2, an interlayer insulatingfilm 13 of SiO₂ formed between the interconnection layer 12 and thesecond gate electrode 10, an interlayer insulating film 14 of SiO₂formed between the first gate electrode 8 and the storage node 81,conductive layers 15a, 15b, and 15c electrically connected onto the cellplate 83 and the source/drain regions 5, an insulating film 16 of asilicon nitride film formed on the conductive layers 15a, 15b, and 15c,an interconnection layer 18 electrically connected to the first gateelectrode 8, an interconnection layer 17 electrically connected to thesecond gate electrode 10, an interlayer insulating film 90 of SiO₂formed to cover the entire surface and having contact holes 90a, 90b,90c, 90d, 90e in the interconnection layer 17, the conductive layer 15b,the interconnection layer 18, the conductive layer 15a and theconductive layer 15c, respectively, a metal interconnection layer 85electrically connected to the interconnection layer 17 in the contacthole 90a, a metal interconnection layer 84 electrically connected to thecell plate 83 through the conductive layer 15b in the contact hole 90b,a word line 86 electrically connected to the interconnection layer 18 inthe contact hole 90c (see FIG. 49), a bit line 87 electrically connectedto the conductive layer 15a in the contact hole 90d (see FIG. 49), and ametal interconnection layer 88 electrically connected to theinterconnection layer 12 in the contact hole 90e through the conductivelayer 15c.

The storage node 81, the capacitor insulating film 82, and the cellplate 83 constitute a stacked type capacitor for storing chargecorresponding to a data signal. The source/drain regions 4, thesource/drain regions 5, the cylindrical portion 2, the first gateelectrode 8, and the second gate electrode 10 constitute a memory celltransistor. Also in the DRAM in accordance with the third embodiment, aswith the first embodiment illustrated in FIG. 1, controlling voltageapplied to the first gate electrode 8 and the second gate electrode 10permits the threshold voltage of the memory cell transistor to be easilycontrolled. Since the memory cell transistor herein has a function ofconducting a switching operation for holding data storage, its thresholdvoltage must be set higher than those of transistors in peripheralcircuitry (not shown). If, for example, the threshold voltage of a fieldeffect transistor in a peripheral circuit is 0.6 V, the thresholdvoltage of the memory cell transistor is preferably about 0.8 V. In thisembodiment, the threshold voltage of the memory cell transistor canreadily be controlled to be 0.8 V using the first gate electrode 8 andthe second gate electrode (sub gate electrode) 10. More specifically, ifthe second gate electrode 10 is fixed to 0 V, the threshold voltagebecomes 0.6 V. If the second gate electrode 10 is fixed to a -0.4 Vlevel, the threshold voltage of the memory cell transistor becomes 0.8V. In other words, a negative voltage (-0.4 V) twice the amount to beincreased from the threshold voltage (0.2 V) is applied to the secondgate electrode 10. This makes it possible to readily set the thresholdvoltage of the memory cell transistor higher than that of the thresholdvoltage of the transistor of the peripheral circuit. Thus, the memorycell transistor having the threshold voltage suitable for a data memoryholding portion can be provided. In the equivalent circuit diagram inFIG. 50, a metal interconnection layer 88 is for providing the back gatevoltage V_(BB) to the p⁺ impurity region 6.

FIG. 51 is a plan view showing arrangement of a plurality of the onememory cell shown in FIG. 47 in practice. Referring to FIG. 51, a bitline 87a represents the i-th bit line, while a word line 86a representsthe j-th word line. Interconnection layers 84a, 84b, and 84c representinterconnection layers to the cell plates, while interconnection layers85a and 85b represent interconnection layers to the second gateelectrodes (sub gate electrodes). The dotted line in the figurerepresents the boundaries between the regions occupied by the memorycells. As described above, arranging one memory cell in the center of arectangular hexagon provides arrangement of one memory cell surroundedby six memory cells. Consequently, the memory cell group attains the"closest packed structure" allowing maximum improvement of integrationdensity.

FIGS. 52-63 are cross sectional views for use in illustration of amanufacturing process of the DRAM in accordance with the thirdembodiment shown in FIGS. 47-50. Referring to FIGS. 47-49 and FIGS.52-63, the manufacturing process of the DRAM in accordance with thethird embodiment will be described.

In the same process as the MIS semiconductor device in accordance withthe first embodiment shown in FIGS. 4 to 21, a structure shown in FIG.52 is formed. More specifically, a structure corresponding to FIG. 21 isthe structure given in FIG. 52.

As shown in FIG. 53, resist 91 to cover the inside of the cylindricalportion 2 is formed. Using the resist 91, a silicon nitride film 32, andsidewalls 39a and 42a of silicon nitride films as mask, a silicon oxidefilm 41 positioned outside the cylindrical portion (see FIG. 52) isetched. An interlayer insulating film 13 is thus formed in the outersurface of a cylindrical second gate electrode 10. Thereafter, theresist 91 is removed away.

As shown in FIG. 54, using the silicon oxide film 41, the siliconnitride film 32, the sidewalls 39a and 42a of silicon nitride films asmask, p type impurity ions are implanted into a p type monocrystallinesilicon substrate 1. Thus, the potential of the substrate is fixed and ap⁺ impurity region 6 having a function of isolating elements is formed.A polycrystalline silicon film (not shown) is formed on the entiresurface as to the extent the outside of the cylindrical portion 2 isburied by means of CVD. After planarizing the polycrystalline siliconfilm, the polycrystalline silicon film is etched back until the siliconnitride film 32, and the sidewalls 39a and 42a are exposed, and thepolycrystalline silicon film inside the cylindrical portion 2 iscompletely removed away. Thus, an interconnection layer 12 to the p⁺impurity region 6 for fixing the potential of the substrate is formed.Thereafter, a silicon oxide film 92 is formed on the entire surface bymeans of chemical vapor deposition.

As shown in FIG. 55, resist 93 covering the outside of the cylindricalportion 2 is formed by means of a photolithography technique. Using theresist 93, the silicon nitride film 32, and the sidewalls 39a and 42a ofsilicon nitride films as mask, the silicon oxide films 91 and 41 (seeFIG. 54) inside the cylindrical portion 2 are etched away. Thus, aninterlayer insulating film 14 covering the inner surface of thecylindrical first gate electrode 8 is formed. Thereafter, the resist 93is removed away.

Then, as shown in FIG. 56, after a polycrystalline silicon film (notshown) is deposited on the entire surface by means of CVD, the surfaceof the polycrystalline silicon film is planarized. Then, thepolycrystalline silicon film is etched back until the upper part of thecylindrical portion 2 is exposed. Thus, a polycrystalline silicon film81a is formed.

As shown in FIG. 57, a silicon oxide film 94 is formed on the entiresurface by means of chemical vapor deposition. A silicon nitride film 95is formed on the silicon oxide film 94. After forming a silicon oxidefilm 96 on the silicon nitride film 95, the surface is planarized. Thus,the silicon nitride film 95 positioned in the upper part of thecylindrical portion 2 is exposed.

As shown in FIG. 58, the silicon nitride film 95 positioned in the upperpart of the cylindrical portion 2 is removed away by a chemicaltreatment. The entire silicon oxide film 96, and the silicon oxide films92 and 94 positioned in the upper part and the sidewall of thecylindrical portion 2 are etched away.

As shown in FIG. 59, after depositing a silicon nitride film (not shown)on the entire surface, a sidewall 96 of a silicon nitride film is formedon the sidewall portion of the sidewall 42a of silicon nitride film, byconducting an anisotropic etching.

As shown in FIG. 60, resist 97 covering the outside of the cylindricalportion 2 is formed by means of a photolithography technique. Using theresist 97, the silicon nitride film 32, and the sidewalls 39a, 42a, and96 of silicon nitride film as mask, the silicon oxide film 94 and thepolycrystalline silicon film 81a (see FIG. 59) are etched. Thus, acylindrical storage node 81 constituting a capacitor lower electrode isformed. Then, the resist 97 is removed away.

As shown in FIG. 61, a capacitor insulating film 82 is formed on theinner surface of the storage node 81. A polycrystalline silicon film(not shown) is formed on the entire surface by CVD, and then the surfaceof the polycrystalline silicon film is planarized. The polycrystallinesilicon film is etched until the upper part of the cylindrical portion 2is exposed. Thus, a cell plate 83 constituting a capacitor upperelectrode is formed. Thereafter, the silicon oxide films 92 and 94 areremoved away by a chemical treatment. The manufacturing process afterthat is the same as the manufacturing process of the first embodimentshown in FIGS. 26-44. The structure corresponding to FIGS. 43 and 44according to the first embodiment is a structure shown in FIGS. 62 and63. Thus, the memory cell portion of the DRAM in accordance with thethird embodiment is completed.

As in the foregoing, according to the semiconductor device in one aspectof the invention, since a standing wall portion having inner and outersurfaces and extending in a tubular manner is formed in a semiconductorsubstrate, a first tubular gate electrode is formed on the inner surfaceof the standing wall portion with a first gate insulating filmtherebetween, and a second tubular gate electrode is formed on the outersurface of the standing wall portion with a second gate insulating filmtherebetween, the threshold voltage of the transistor can easily becontrolled without requiring change of the materials for the gateelectrodes. As first source/drain regions of second type conductivityare formed on the top ends of the standing wall portion, and a secondsource/drain region of the second type conductivity is formed on thebottom surface of the semiconductor substrate surrounded by the innersurface of the standing wall portion, and the side portion of thestanding wall portion can be utilized as a channel region as well asarea occupied by the elements can be reduced as compared to conventionalplanar type (plane type) transistors. Consequently, a semiconductordevice suitable for high density integration can be provided.

Furthermore, according to a semiconductor device in another aspect ofthe invention, since a standing wall portion having inner and outersurfaces and extending in a tubular manner is formed in a semiconductorsubstrate, a first gate electrode is formed on the inner surface of thestanding wall portion with a first gate insulating film therebetween, asecond gate electrode is formed on the outer surface of the standingwall portion with a second gate insulating film therebetween, firstsource/drain regions of second type conductivity are formed on the topends of the standing wall portion, a second source/drain region of thesecond type conductivity is formed on the bottom surface of thesemiconductor substrate surrounded by the inner surface of the standingwall portion, a capacitor lower electrode electrically connected to thesecond source/drain region is formed, and a capacitor upper electrode isformed on the capacitor lower electrode with a capacitor insulating filmtherebetween, the threshold voltage of the transistor can easily becontrolled by voltage applied to the second gate electrode. Also, theside surface of the standing wall portion can also be used for thechannel region of the transistor, area occupied by the elements canreduced as compared to conventional planar type transistors, thusallowing high density integration. Furthermore, since the capacitorformed of the capacitor lower electrode, the capacitor insulating film,and the capacitor upper electrode is connected to the secondsource/drain region of such a transistor, threshold voltage of thememory cell transistor can easily be controlled at a threshold voltagelevel suitable for holding the data of the capacitor, and a memory cellsuitable for high density integration can be provided.

According to a method of manufacturing the semiconductor device in oneaspect of the invention, since a standing wall portion having inner andouter surfaces and extending in a tubular manner is formed in a mainsurface of a semiconductor substrate of first type conductivity, a firsttubular gate electrode is formed on the inner surface of the standingwall portion with a first gate insulating film therebetween, a secondtubular gate electrode is formed on the outer surface of the standingwall portion with a second gate insulating film therebetween, firstsource/drain regions are formed by implanting an impurity of second typeconductivity into the top end portions of the standing wall portion, andan impurity of the second type conductivity is implanted into the bottomsurface of the semiconductor substrate surrounded by the inner surfaceof the standing wall portion to form a second source/drain region, thethreshold voltage of the transistor can easily be controlled using thefirst gate electrode and the second gate electrode, a semiconductordevice which utilizes the side surface of the standing wall portion as achannel region and suitable for high density integration can bemanufactured.

According to a method of manufacturing a semiconductor device inaccordance with another aspect of the invention, since a standing wallportion having inner and outer surfaces and extending in a tubularmanner is formed on a main surface of a semiconductor substrate of firsttype conductivity, a first tubular gate electrode is formed on the innersurface of the standing wall portion with a first gate insulating filmtherebetween, a second tubular gate electrode is formed on the outersurface of the standing wall portion with a second gate insulating filmtherebetween, a first source/drain region is formed by implanting animpurity of second type conductivity to the top end of the standing wallportion, a second source/drain region is formed by implanting animpurity of the second type conductivity into the bottom surface of thesemiconductor substrate surrounded by the inner surface of the standingwall portion, a capacitor lower electrode is formed to be electricallyconnected to the second source/drain region, and a capacitor upperelectrode is formed on the capacitor lower electrode with a capacitorinsulating film therebetween, the threshold voltage of the transistorcan readily be controlled by the first gate electrode and the secondgate electrode, and a semiconductor device which utilizes the sidesurface of the standing wall portion as the channel region of thetransistor and suitable for high density integration can be provided.Furthermore, combining such a transistor and such a capacitor provides asemiconductor device having memory cells suitable for high densityintegration.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. A method of manufacturing a semiconductor device,comprising the steps of:forming a standing wall portion having inner andouter surfaces and extending in a tubular manner on a main surface of asemiconductor substrate of first type conductivity; forming a firsttubular gate electrode on the inner surface of said standing wallportion with a first gate insulating film therebetween; forming a secondtubular gate electrode on the outer surface of said standing wallportion with a second gate insulating film therebetween; forming a firstsource/drain region by implanting a first impurity of second typeconductivity to the top end of said standing wall portion; and forming asecond source/drain region by implanting a second impurity of the secondtype conductivity to the bottom surface of said semiconductor substratesurrounded by the inner surface of said standing wall portion.
 2. Amethod of manufacturing a semiconductor device as recited in claim 1,whereinsaid step of forming the standing wall portion includes a step offorming a cylindrical standing wall portion extending from the mainsurface of said semiconductor substrate in a direction approximatelyvertical to the main surface of said semiconductor substrate.
 3. Amethod of manufacturing a semiconductor device, comprising the stepsof:forming a standing wall portion having inner and outer surfaces andextending in a tubular manner on a main surface of a semiconductorsubstrate of first type conductivity; forming a first tubular gateelectrode on the inner surface of said standing wall portion with afirst gate insulating film therebetween; forming a second tubular gateelectrode on the outer surface of said standing wall portion with asecond gate insulating film therebetween; forming a first source/drainregion by implanting a first impurity of second type conductivity to thetop end of said standing wall portion; forming a second source/drainregion by implanting a second impurity of the second type conductivityto the bottom surface of said semiconductor substrate surrounded by theinner surface of said standing wall portion; forming a capacitor lowerelectrode to be electrically connected to said second source/drainregion; and forming a capacitor upper electrode on said capacitor lowerelectrode with a capacitor insulating film therebetween.
 4. A method ofmanufacturing a semiconductor device as recited in claim 3, whereinsaidstep of forming the capacitor lower electrode includes a step of forminga tubular capacitor lower electrode extending in a directionapproximately vertical to the main surface of said semiconductorsubstrate.